Vibration isolating bushing and its manufacturing method

ABSTRACT

This invention relates to a vibration isolating bushing, for example, built into a suspension system, an inside diameter of one edge ( 4 ) of an inner cylinder ( 1 ) being made larger than that of the other edge ( 6 ). The outside diameter of the thinner edge ( 4 ) is enlarged by applying pressure with a pressure forming jig( 26 ) to the thicker edge surface ( 25 ), with the thinner edge surface ( 20 ) of the inner cylinder ( 1 ) abutted on a base ( 23 ). After completion of enlargement of the outside diameter of the thinner edge ( 4 ), the outside diameter of the thicker edge ( 6 ) is enlarged by further pressure with the pressure forming jig ( 26 ), this process thus capable of enlarging the outside diameter of both edges ( 4 ), ( 6 ) with one continuous working step. Surface unit pressure applied by another member can be made smaller by enlarging the outside diameter of the thinner edge ( 4 ), and the outer cylinder ( 2 ) can be prevented from being slipping out from the inner cylinder through the enlargement of the outside diameter of the thicker edge ( 6 ).

FIELD OF THE INVENTION

This invention relates to a vibration isolating bushing, for example,built in a part of a suspension system of an automobile, to controlvibration, etc. propagated from wheels to the vehicle body, and to itsmanufacturing method.

DESCRIPTION OF THE RELATED ART

In general, in an automobile such as a passenger car, a vibrationisolating bushing has been built as part of the suspension system or thesupport mechanism of the engine, so as to control vibration propagatedfrom the wheels to the vehicle body or vibration etc. from the engine tothe vehicle body.

FIG. 9 shows an example of vibration isolating bushing. The vibrationisolating bushing comprises a metal inner cylinder 101, an outercylinder 102 disposed outside the inner cylinder with an intervalbetween them, and a rubber elastomer 103 interposed between the innerand outer cylinders 101, 102, the inner and outer cylinders 101, 102each fixed respectively to another member to connect these two membersso that vibration is isolated.

The inner cylinder 101 has an inside diameter which is nearly constantalong the axial direction, with a shaft member inserted inside, and isfastened to attachment members such as brackets, in the state that bothextremities 104 are held between attachment members or that only one ofthe extremities 104 is abutted to an attachment member.

At both edges 105 of the inner cylinder 101, enlarging of the outsidediameter to enlarge the areas of both extremities 104 has been carriedout to reduce the surface pressure between the edge surface 104 and theattachment member when the two are fastened. In addition, since theoutside diameter of both edges 105 is enlarged and becomes larger thanthe inside diameter of the outer cylinder 102 disposed around thecentral portion of the inner cylinder 106, the outer cylinder 102 isprevented from slipping away from the inner cylinder 101 when the rubberelastomer 103 deforms excessively.

FIG. 10 shows the process of extending both extremities 105 of the innercylinder 101. This extending work is performed to depress the pressurewelding surface 108 of a pressure forming jig 107 upon the extremities104 of the inner cylinder 101 and then make the pressure forming jig 107rotate. This extending work is carried out at every edge 105 to extendthe outside diameter of both edges 105.

Incidentally, when the inner cylinder 101 of the vibration isolatingbushing is fixed to a member on the wheel side, the inner cylinder 101may be fixed by inserting into it a bolt extending from the back side ofthe member, etc., with the extremities 104 of the inner cylinder 101abutted with the member. In this case, since it is difficult to insertthe bolt in the inner cylinder 101, it takes a long time to install thevibration isolating bushing, which has caused increase in cost.

Both edges 105 of each inner cylinder 101 are worked individually.Therefore, after one edge 105 has been worked, the pressure forming jig107 must be removed and orientation of the inner cylinder 101 bereversed, and the pressing welding jig 107 must be set up again beforeworking the other edge 105. This causes prolonged working time andincrease in cost.

DISCLOSURE OF THE INVENTION

Starting with a vibration isolating bushing comprising a metal innercylinder, an outer cylinder disposed outside the inner cylinder with aninterval between them, and a rubber elastomer interposed between theinner and outer cylinders, the present invention provides a vibrationisolating bushing that facilitates a bolt to be inserted into the innercylinder from one end by making the inside diameter at one end in theaxial direction of the inner cylinder larger than that at the centralportion and at the other end, and also provides the manufacturing methodof the vibration isolating bushing.

If the outside diameter at both edges of the inner cylinder is largerthan that at the central portion, the pressure at the surface of theattachment member and the edge of the inner cylinder contacting eachother is reduced, and it is possible to prevent the abutting surface ofan attachment member from being depressed, prevent the contacting edgeof the inner cylinder from buckling and the like, as well as preventingthe outer cylinder from slipping out in the direction of the other end.

That is, when the outside diameter of the inner cylinder is constantalong the axial direction, the area of one edge surface becomes smallerby making the inside diameter of that edge larger, and the area of oneedge surface is made larger by making the outside diameter of that edgelarger so as to make the surface pressure smaller. Further, the otherside edge, the outside diameter of which is made larger, can be made toact as a stopper to restrain the outer cylinder from slipping out.

An inner cylinder the outside diameter at both edges of which is largerthan that of the central portion can be formed by enlarging the outsidediameter of both edges of a metal cylindrical body whose inside diameterat one edge is larger than that at the central portion and at the otheredge, and whose outside diameter is initially nearly constant in theaxial direction.

In other words, the metal cylindrical body whose thickness at one edgeis made thinner than that of the central portion and the other side edgecan, in the enlarging of the outside diameter of both edges, be workedmore simply, starting from the edge which is not thinner.

Concretely, the outside diameter at the thinner edge, the thickness ofwhich is thinner than at the other side edge, will be enlarged byabutting the former edge surface against a base and then making thepressure forming jig put pressure on the thicker edge surface. Whenkeeping the pressure forming jig pressure on the thicker edge surfaceafter completion of working of the thin edge, the outside diameter atthe other side edge also will be enlarged.

If an inner die is fitted into the inner circumference of the thin edgewhen abutting that edge surface of the cylindrical body against thebase, that edge can be prevented from buckling, the outside diameterwill be enlarged without diminishing in diameter the inside diameter ofthe thin edge. Further, when the outer circumference of the thin edge isenclosed at a predetermined interval by an outer die, the outsidediameter after enlarging can be made to be the predetermined size.

If one edge is made thinner than the sleeve at the central portion andthe other edge, this working method can be adapted to any metalcylindrical body, not limited to the inner cylinder of the vibrationisolating bushing. Further, the outside diameter of the cylindrical bodyneed not be nearly constant along the axial direction.

A working apparatus equipped with a base abutting on the thinner edgesurface of the cylindrical body, an outer die enclosing that edge of thecylindrical body and a pressure forming jig putting pressure on thethicker edge surface of the cylindrical body, may be used.

As for the base, the inner die fitted to the inner circumference of thecylindrical body may be provided on the abutting surface against whichone edge surface of the cylindrical body is abutted. Consequently, sincethe inner die can be fitted concurrently when the cylindrical body isabutted on the base, the inner die can be made to impede slippage of thecylindrical body on the base during working.

The outer die may be of two detachable halves and freelydetachable/attachable to the base, and an opening may be provided so asto enclose one edge of the cylindrical body at predetermined intervalwith it, in the state of being attached to the base. Since the outer dieis of two detachable halves, there will be no problem with thecylindrical body whose outside diameter has enlarged being stuck in theouter die. Besides, attaching to the base can impede slippage from theinner die so that the thickness of the cylindrical body will not bevariable after enlarging.

The pressure forming jig is formed to have a pressure contact surfacethat puts pressure on the thicker edge of the cylindrical body, and thispressure contact surface may be part of the surface of a circular cone.In this case, when the pressure forming jig is disposed so that the apexof the circular cone lies at the center of the thicker end of thecylindrical body and is turned, pressure is applied to the entirethicker edge.

To manufacture the vibration isolating bushing, the inside diameter ofthe one edge is first made larger than that of the central portion andof the other edge with the outer diameter kept roughly constant, theouter cylinder is disposed around the inner cylinder with rubberelastomer between the two. Incidentally, the outside diameter at bothedges of the inner cylinder may be enlarged according to theaforementioned working method. By doing so, when the edge surface diesare taken out after vulcanization forming of the rubber elastomer, bothedges, the outside diameter of which are not yet enlarged, do not get inthe way.

In the same manner as the aforementioned working method, when abuttingthe thin edge surface of the inner cylinder against the base, the innerdie may be fitted to the inner circumference of the thin edge and theouter circumference of the thin edge may be enclosed by the outer die sothat there is a predetermined interval between the two.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial sectional view of a vibration isolating bushing ofthe present invention.

FIG. 2(a) is a plan view of a link support member attached to the wheelside member and FIG. 2(b) is its front view.

FIG. 3 is an axial sectional view of the vibration isolating bushingattached to the wheel side member.

FIG. 4 is an axial sectional view of the vibration isolating bushingbefore working the inner cylinder.

FIG. 5 is an exploded view of a working apparatus of the inner cylinder.

FIG. 6 is an axial sectional view of an outer die.

FIG. 7 is a front view of principal parts of pressure forming jig.

FIG. 8 is an axial sectional view showing the method of working theinner cylinder: FIG. 8(a) shows the inner cylinder before working andFIG. 8(b) shows after working.

FIG. 9 is an axial sectional view of conventional vibration isolatingbushing.

FIG. 10 is an axial sectional view showing conventional method ofworking the inner cylinder of the vibration isolating bushing.

BEST MODE FOR CARRYING OUT THE INVENTION

Best mode for carrying out the present invention will be hereinafterdescribed with reference to the drawings. As shown in FIG. 1, thevibration isolating bushing of the present embodiment comprises a metalinner cylinder 1, an outer cylinder 2 disposed around the inner cylinderwith an interval between the two, and a rubber elastomer 3 interposedbetween the inner and outer cylinders 1, 2. The inner and outercylinders 1, 2 are each fixed respectively to another member, to connectboth members for the purpose of vibration isolation.

The inner cylinder 1 is, for example, a steel cylinder, the insidediameter (d1) of one edge 4 being larger than the inside diameter (d2)of the central portion 5 and of the other edge 6, so that a bolt 21 iseasily inserted through the one end. Further, in order to eliminate thestep at the inner surface at the boundary of the portion near the thinedge 4 with larger inside diameter and the center portion with smallerinside diameter, a portion tapering along the axial direction 7 isformed. Thus the bolt inserted will not get caught midway.

Female threads 8 are cut on the inner circumferential surface of thecentral portion 5 nearer to the edge 4, so as to screw the bolt 21inside the inner cylinder 1 from the edge 4. The outside diameter (D1,D2) of both edges 4, 6 of the inner cylinder 1 are larger than theoutside diameter (D3) at the central portion.

The outer cylinder 2 is, for example, of a steel cylindrical form, theaxial length of which is nearly the same as the central portion 5 of theinner cylinder 1, and disposed outside of the central portion 5 of theinner cylinder 1. The inside diameter (d3) of the outer cylinder 2 islarger than the outside diameter (D3) of the central portion 5 of theinner cylinder 1 so that the rubber elastomer 3 can be interposedbetween the outer cylinder 2 and the inner cylinder 1.

At for one edge 9 of the outer cylinder 2, the portion very close tothis edge is enlarged outwardly, and then the edge is again reduced indiameter so that it bulges out close to the edge, this bulge serving asa stopper when the outer cylinder 2 is press fitted into the opening 13of another part. Since the inside diameter (d4) of this edge 9 issmaller than the outside diameter (D2) of the edge of the inner cylinder1 in the same direction 6, the outer cylinder 2 will not slip out fromthis end of the inner cylinder 1.

The rubber elastomer 3 is in the form of a ring, interposed between theouter surface of the central portion 5 of the inner cylinder 1 and theinner surface of the outer cylinder 2 by vulcanization forming, joinsthe inner and outer cylinders 1, 2, and serves to dampen vibration, etc.propagated between them. On one end of the rubber elastomer 3, a concaveindentation 10 is formed to adjust the spring constant according to thedirection of deformation.

The vibration isolating bushing is, for example, used for attachment oflink support member 11 to a member 12 connected to the wheel, as shownin FIG. 2. The link support member 11 supports the one end of the linkrestraining the fore-and-aft relative movement between the member 12 andthe vehicle frame.

The opening 13, in which the outer cylinder 2 of the vibration isolatingbushing is press fitted, is provided at the one end side of the linksupport member 11, and the link support member 11 is attached to themember 12 via the vibration isolating bushing. Further, anothervibration isolating bushing 14 is attached to the opening at the otherend side of the link support member 11, and the link is supportedthrough the vibration isolating bushing 14.

FIG. 3 shows the vibration isolating bushing inserted into the opening13 of the link support member 11 and attached to the member 12connecting to the wheel. A portion 15 of the member 12 attaching to thevibration isolating bushing is made up of upper/lower flanges 17, 18forming a hole 16 for the bolt, and a reinforcing ring 19 interposedbetween the upper/lower flanges 17, 18 surrounding the hole 16.

On the top surface of the upper flange 17, one edge surface 20 of theinner cylinder 1 is abutted in alignment with the reinforcing ring 19. Abolt 21 inserted from below the lower flange 18 is screwed into thefemale threads 8 of the inner cylinder 1 to fasten and secure the innercylinder 1 to the top surface of the upper flange 17. On the other hand,the outer cylinder 2 is press fitted and secured into the opening 13 ofthe link support member 11, and the link support member 11 is attachedto the top surface of the member 12.

Since the inside diameter (d1) at one edge 4 of the inner cylinder 1 islarger than the inside diameter (d2) of the central portion 5 and of theother edge 6 according to the configuration described above, the bolt 21is easily inserted into the inner cylinder 1 from below the member 12.

Further, since the outside diameter (D1) of the edge 4 is larger thanthat (D3) of the central portion 5, the thickness of the edge 4(D1/2-d1/2) can be made as predetermined even when the inside diameter(d1) of the edge 4 is made larger. Accordingly, since the area of theedge surface 20 can be increased, the surface pressure, when the innercylinder 1 is fastened to the member 12 by the bolt 21, is made lessthan the predetermined value to prevent the member 12 from beingdepressed and the edge 4 from buckling.

Furthermore, since the outside diameter (D2) of the thicker edge 6 ofthe inner cylinder 1 is larger than the inside diameter (d4) at the edge9 of the outer cylinder 2 in the same direction, it is possible toprevent the outer cylinder 2 from slipping out of the inner cylinder 1in this direction when the rubber elastomer 3 is deformed excessively.The member 12 impedes the outer cylinder 2 from slipping out from theother end of the inner cylinder 1.

Next, the manufacturing method of the vibration isolating bushing isdescribed below. As shown in FIG. 4, the inner cylinder 1 is formed, forexample, by steel forging. As for the inner cylinder 1, the insidediameter (d1) of the thinner edge 4 is larger than that (d2) of thecentral portion 5 and of the thicker edge 6, the outside diameter (D3)thereof is made to be constant along the axial direction, and thethickness of the thinner edge 4 (D3/2-d1/2) is thinner than that(D3/2-d2/2) of central portion 5 and the thicker edge 6.

The outer cylinder 2 is disposed around the central portion 5 of theinner cylinder 1, and the rubber elastomer 3 is interposed between theinner and outer cylinders 1, 2 by vulcanization forming. Then, theoutside diameter (D3) of both edges 4, 6 of the inner cylinder 1 isenlarged to (D1), (D2), respectively, by the shaping apparatus 22 toform the predetermined shape.

The configuration of the working apparatus 22 is described below. Asshown in FIG. 5, the shaping apparatus 22 comprises a base 23 abuttingon the thinner edge surface 20 of the inner cylinder 1, an outer die 24enclosing the thinner edge 4 of the inner cylinder 1, and a pressureforming jig 26 exerting pressure on the thicker edge surface 25 of theinner cylinder 1.

The base 23 is, for example, of higher strength steel than the innercylinder 1, and an outer die attachment portion 28 of circular crosssection is formed at the top surface side of the foundation portion 27.The top surface 29 of the outer die attachment portion 28 is a surfaceabutting against the thinner edge surface 20 of the inner cylinder 1,and an inner die 30 of circular cross section fitting on the innercircumference of the inner cylinder 1 is provided at the center of theabutting surface 29. The outside diameter (D4) of the inner die 30 isslightly smaller than the inside diameter (d1) of thinner edge 4 of theinner cylinder 1, and its tip portion 31 is continuously tapered tomatch the taper 7 of the inner cylinder 1.

The outer die 24 is, for example, of higher strength steel than theinner cylinder 1, and freely detachable/attachable to the outer dieattachment portion 28 of the base 23. The outer die 24 is made up of acylindrical portion 32 and a lid portion 33 covering the top of thecylindrical portion 32, and attached to the outer die attachment portion28 by fitting the cylindrical portion 32 around the outer die attachmentportion 28 and abutting the bottom surface of the lid portion 33 againstthe abutting surface 29. The outer die 24 is divided axially into two,and the halves 24 a, 24 b are made into one by joining them at a joiningarea (not shown) when attaching to the outer die attachment portion 28of the base 23.

An opening 34, the diameter (D1) of which is larger than the outsidediameter (D3) of the inner cylinder 1 prior to working, is formed at thecenter of the lid portion 33, and the opening 34 encloses the inner die30 with the predetermined clearance left when fitting the lid portion33. As shown in FIG. 6, the diameter of the opening 34 is nearlyconstant from near the center to the upper surface, and grows largerfrom near the center to the lower surface. That is, the innercircumference 35 of the opening 34 is formed to accord with the intendedouter surface of the inner cylinder 1 near the thinner edge 4 afterbeing worked.

As shown in FIG. 7, the pressure forming jig 26 is, for example, ofhigher strength steel than the inner cylinder 1, and the pressurewelding surface 37 in the shape of a section of a circular cone and putin pressure contact with the thicker edge surface 25 of the innercylinder 1, is circumferentially continuously formed at the bottom endof the pressure forming jig body 36 of circular cross section. Aprotrusion 38 is formed at the center of the pressure welding surface 37to insert into the inside of the inner cylinder 1 to keep the pressureforming jig 26 from slipping with respect to the inner cylinder 1 aswell as to keep the inside diameter of the thicker edge 6 of the innercylinder 1 from being diminished in diameter.

Next, the procedure of enlarging the outside diameter of both edges 4, 6of the inner cylinder 1 using the working apparatus 22 is describedbelow. First, as shown in FIG. 8(a), with the inner die 30 fitted to theinner circumferential side of the thinner edge 4 of the inner cylinder1, the thinner edge surface 20 of the inner cylinder 1 is abutted to theabutting surface 29 of the base 23. With the outer die 24 attached tothe outer die attachment portion 28 of the base 23, the outercircumferential side of the thinner edge 4 of the inner cylinder 1 isenclosed by the opening 34 with the predetermined clearance left.

Next, as shown in FIG. 8(b), with the protrusion 38 of the pressureforming jig 26 is inserted into the inside of the thicker edge 6 of theinner cylinder 1, and with an apex 39 of the pressure welding surface 37located at the center of the thicker edge surface 25 of the innercylinder 1, the pressure welding surface 37 of the pressure forming jig26 is abutted to the thicker edge surface 25. The thicker edge surface25 is entirely pressure formed by making the pressure forming jig 26 bein turning motion centering the apex 39.

As for the inner cylinder 1 before being worked, since the thickness ofthe thinner edge 4 is thinner than that of the central portion 5 and thethicker edge 6, larger degree of compressive stress is yielded at thethinner edge 4 when the pressure forming jig 26 is put in pressurecontact on the thicker edge surface 25 of the inner cylinder 1. Due toplastic deformation caused by the degree of compressive stress, theoutside diameter of the thinner edge 4 is enlarged accompanied withcontraction in the axial direction.

Enlargement toward the center (diminishment in inside diameter) isimpeded by compressive force acting circumferentially. That is, when thethinner edge 4 is compressed in the axial direction, compressive forcethereby acts to shorten the circumference. If the thinner edge 4enlarges inwardly, circumferential length shortens accordingly, and thecompressive force acting circumferentially grows larger. Thiscompressive force acts as a radial force pushing out, thereby impedinginward enlargement.

When the inner circumferential surface of the thinner edge 4 abuts onthe circumferential surface of the inner die 30 by means of elasticdeformation which becomes plastic deformation, inward enlargement isrestrained. Consequently, only the outside diameter of the thinner edge4 is enlarged substantially, and there is no case where the inner die 30cannot be pulled out after completion of working.

When the outside diameter of the thinner edge 4 is enlarged to “D1” andits outer circumferential surface abuts on the inner circumferentialsurface 35 of the opening 34 of the outer die 24, further enlargement isrestrained, thus completing enlargement of the outside diameter at thethinner edge 4.

After this, the pressure forming jig keeps putting pressure on thethicker edge surface. At this time, since the outside diameter of thethinner edge 4 cannot be enlarged, the outside diameter of the thickeredge 6, on which the pressure forming surface 37 of the pressure formingjig 26 abuts directly, is enlarged, accompanied with contraction in theaxial contraction due to plastic deformation. Enlargement of the innercylinder 1 is completed when the outside diameter of the thicker edge 6is enlarged to “D2”. The outer die 24 is then removed, and production ofthe vibration isolating bushing is completed. Since the outer die 24 isof two halves, it can be taken out easily from the thinner edge 4 of theinner cylinder 1.

According to the manufacturing method described above, since the outsidediameter of the portion of the inner cylinder located within the outercylinder is nearly constant in the axial direction, and the outsidediameter of both edges 4, 6 of the inner cylinder 1 is enlarged afterthe rubber elastomer 3 between the inner and outer cylinders 1, 2 isvulcanization formed, both edges 4, 6 of the inner cylinder 1 do not getin the way when the dies at the axial extremities required forvulcanization forming of the rubber elastomer 3 are removed.

Besides, since the outside diameter of both edges 4, 5 is enlarged bypressing the pressure forming jig 26 to the thicker edge surface 25 withthe thinner edge surface 20 of the inner cylinder 1 abutted against theabutting surface 29 of the base 23, both edges 4, 5 of the innercylinder 1 can be undergo the pressure formation at one time.

It will be appreciated that the present invention is not limited to thebest mode for carrying out the invention described, but variations ormodifications may be made appropriately within the scope of thisinvention. For example, the working method of the inner cylinder can beadopted for any use, not just for the inner cylinder of the vibrationisolating bushing, provided that it is a metal cylindrical body the oneedge of which is thinner than the sleeve of the central portion and theother side edge.

It also may be that the outside diameter of the thicker edge is enlargedwhen the circumference of the thinner edge is enlarged without thethinner edge being enclosed by an outer die, when the thickness of thethinner edge comes close to that of the thicker edge. In the case wherethe thinner edge has enough thickness to prevent buckling, it is notnecessary to use the inner die.

INDUSTRIAL APPLICABILITY

It will be obvious from the description above that, according to thevibration isolating bushing of the present invention, the insidediameter of the thinner edge can be enlarged by enlarging the outsidediameter of both edges of the inner cylinder after vulcanization formingof the rubber elastomer without making the area of the thinner edgesurface of the inner cylinder smaller. Accordingly, for example, whenthe vibration isolating bushing is used for attachment to a member ofthe link support connected to the wheel, the tightening bolt can easilybe inserted, without causing depression of the member on which thethinner edge surface of the inner cylinder abuts, and without bucklingof the thinner edge, thus contributing to shortening of manufacturingtime and cost reduction.

Furthermore, since this is an efficient method capable of enlarging theoutside diameter of both edges by the pressure forming operation at onetime through pressing the pressure forming jig on the thicker edge, itwill contribute to working time shortening and cost reduction.

1. A method of working a metal cylindrical body, the thickness at oneedge of which is made thinner than that of the central portion and theother edge, to enlarge the outside diameter at both edges of the metalcylindrical body, being enlarged by abutting the thinner edge surface ofthe cylindrical body against a base and then applying pressure with thepressure forming jig to the thicker edge surface, and after completionof enlarging of the diameter at the thinner edge, the outside diameterat the other side edge then being enlarged by pressure forming of thethicker edge surface by the pressure forming jig.
 2. The method ofworking the metal cylindrical body as set forth in claim 1, wherein aninner die is fitted at the inner circumference of the thinner edge whenit abuts against the base, whereas the outer circumferential side of thethinner edge is enclosed at a constant predetermined interval by anouter die.
 3. A working apparatus used for the working of the metalcylindrical body as set forth in claim 2, comprising a base abutting onthe thinner edge surface of the cylindrical body, the outer dieenclosing the thinner edge of the cylindrical body, the pressure formingjig pressing on the other edge of the cylindrical body, and on the base,the inner die fitted to the inner circumferential side of thecylindrical body is provided on the abutting surface, against which thethinner edge surface of the cylindrical body is abutted, the outer dieis of two halves and freely detachable/attachable to the base to form anopening enclosing the thinner edge of the cylindrical body at a constantinterval when the outer die is attached to the base, and the pressureforming jig is made up of a section of a circular cone, formed to have apressure contact surface that applies pressure to the thicker edgesurface of the cylindrical body.
 4. A vibration isolating bushingcomprising a metal inner cylinder, an outer cylinder disposed around theinner cylinder with an interval between them, and a rubber elastomerinterposed between the inner and outer cylinders, the inside diameter atthe one edge of the inner cylinder being made larger than that at thecentral portion and the other side edge, and the outside diameter ofboth edges being made larger than that of the central portion.
 5. Amethod of manufacturing the vibration isolating bushing as set forth inclaim 4, wherein the inside diameter of the thinner edge is made largerthan that at the central portion and the other side edge, the outercylinder being disposed via the rubber elastomer around the innercylinder, the outside diameter of which is nearly constant along theaxial direction, and the outside diameter at the thinner edge, thethickness of which is thinner than at the other side edge, beingenlarged by abutting the thinner edge surface of the inner cylinderagainst the base and applying pressure with the pressure forming jig tothe thicker edge surface, and after completion of enlargement of thethinner edge, the outside diameter of the thicker edge being enlarged byputting further pressure on the thicker edge surface with the pressureforming jig.
 6. A method of manufacturing the vibration isolatingbushing as set forth in claim 5, wherein, when abutting one edge surfaceof the inner cylinder against the base, the inner die is fitted at theinner circumference of the thinner edge, and the outer circumference ofthe thinner edge is enclosed at a constant predetermined interval by theouter die.